Device for coating a substrate by means of plasma-CVD or cathode sputtering

ABSTRACT

A device for covering a substrate by means of both plasma chemical vapor deposition and by high-frequency cathode sputtering which, as a result of easily exchangeable individual devices to introduce gaseous substances into the reaction space as well as easily exchangeable individual devices for influencing the flow of the process gases within the reaction space, results in a very good uniformity of the layer thickness of the produced layers even when the operation has to be carried out at higher gas pressures and hence higher flow rates.

This is a division of application Ser. No. 694,725 filed Jan. 25, 1985,now U.S. Pat. No. 4,673,588.

BACKGROUND OF THE INVENTION

The invention relates to a device for coating a substrate by means ofplasma-chemical vapour deposition or cathode sputtering, said devicehaving an evacuated chamber, a first and a second electrode, means forintroducing gaseous substances into the chamber, and means for applyingan RF-voltage to the first and/or the second electrode to produce aplasma.

Such a device may be used, for example, for coating a substrate with alayer of polymerized material by a glow discharge polymerization or alsoas a device for a cathode sputtering process.

Glow discharge polymerization is a known technique for depositing alayer of an organic or inorganic polymer. There are two fundamentaltypes of methods.

In the first type the surface of an existing material is polymerized andcured by being exposed to a glow discharge which is produced in air orin an inert gas. Surface molecules are activated by the glow dischargeand form compounds and cross-linked compounds with adjacent molecules.Since the activation is limited to an area in the proximity of thesurface, the mass of the material remains unchanged. In the second typeof method a different layer of polymerized material is deposited on asubstrate by a glow discharge that is produced in a monomeric gasadjoining the substrate. Reactive species and types of material,respectively, which are produced in the glow discharge are deposited onthe substrate and form a polymerized layer. The polymerization extendsthrough the whole deposited material. The present device relates to theperformance of polymerization methods of the second type.

In a typical polymerization situation of the second type the flowdischarge is produced by means of an electric potential which is appliedto two electrodes which are provided in a space which comprises amonomeric gas at a pressure less than atmospheric pressure. A glowdischarge occurs and only a very small current flows through the gas,when the potential between the electrodes does not exceed a thresholdvalue, which value is sufficient to produce ionization of the gas ordisruptive discharge.

It is known that this discharge potential depends on the composition ofthe gas, the pressure of the system and the spacing between theelectrodes. After the discharge has occurred, the gas is conductive anda stable plasma can be maintained over a wide current range. Once aplasma has been produced, it can be maintained by a potential which issmaller than the breakdown potential and the breakdown voltage,respectively. The accurate composition of the discharge plasma is notknown. It is assumed that it consists of electrons, ions, free radicalsand other reactive species.

Cathode sputtering is also a known method for forming a layer ofmaterial on a substrate.

In cathode sputtering the material is removed from the surface of atarget plate by ion bombardment and is deposited on the substrate. Whenthe material to be sputtered is electrically conductive, a directvoltage potential is used. When the material to be sputtered is notelectrically conductive or is an insulator, it is preferred to use ahigh frequency voltage to avoid the formation of surface charges on theinsulator and the loss of accelerating voltage resulting therefrom. Inknown methods of depositing a layer of a polymer by cathode sputtering,first the polymer itself is prepared in the form of a sheet,respectively, or a powder target. A target electrode is manufactured byarranging the target in contact with a conductive surface. The targetelectrode and the target, respectively, and a second electrode areprovided in an evacuated space which may be filled with an ionizableinert gas, for example argon, at a suitable pressure. A polymeric layercan be formed on a substrate by a glow discharge which is produced byapplying a suitable voltage between the target and the second electrode.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a device of the kinddescribed in the opening paragraph which may be used both for thedeposition of layers by means of a plasma-chemical vapour depositionprocess and also by means of a cathode sputtering process i.e. an RFcathode sputtering process which allows a great variability of theprocess, which hence can easily be converted into different desiredprocesses, which device can easily be dismantled, which can easily becleaned, and which ensures a particularly good homogeneity of thethickness of the layers to be produced.

According to the invention this object is achieved by a device having anevacuatable chamber provided with a first electrode which is fixed inthe axial direction and has a central aperture (annular electrode) and acounter electrode (sheet electrode), both electrodes arranged centrallyin the evacuatable space, the annular electrode being provided on abipartite insulator block having an upper first portion adjoining theannular electrode, and having a central aperture corresponding to thecentral aperture of the annular electrode and having a second portionimmediately adjoining the first portion and bearing on the base plate ofthe evacuatable chamber over a connection flange of the vacuum pumprequired for the evacuation of the space, said second portion leavingthe connection flange free.

According to an advantageous embodiment of the invention the firstportion of the insulator block is provided with at least one furtheraperture opening into the central aperture and extending approximatelyperpendicularly to the central aperture. By such means the advantage isobtained that the device can very rapidly be converter for use withvarious devices for introducing gaseous substances.

A particularly good adaptability of the process is achieved by makinguse of two different principals for introducing gaseous substances.According to one advantageous further embodiment of the invention thedevice for introducing gaseous substances into the evacuatable chamberis a multichamber annular distributor in which reaction gases can beintroduced from without and can freely reach the reaction space in thechamber. The device for introducing gaseous substances into theevacuatable chamber may also be achieved by gas pipes which areintroduced into the evacuatable chamber in a vacuum-tight manner andopen into the further aperture opening into the central aperture of theinsulator block and extending at right angles to the central aperture.

With the introduction of the gaseous substances via the multichamberannular distributor the advantage is achieved that a very goodhomogenization of the gas flow is ensured, which leads to anextraordinary good uniformity of the layer thickness of the producedlayers. With this gas flow and the possibility of adjusting the heightof the multichamber annular distributor in such manner that the distancebetween the annular electrode and the gas outlet aperture in themultichamber annular distributor is kept as small as possible thefurther advantage is achieved that the pollution of the reactor remainsvery low. This type of gas flow is particularly suitable when theprocess is to be carried out at higher gas pressures and hence higherflow rates, so always when a depletion of the above species as a resultof an increased deposition rate occurs and the adjusting layer thicknessgradient should be avoided.

With the gas flow via the inlet of the gaseous substances immediatelyinto the central aperture in the bipartite insulator block below theannular electrode the advantage is achieved that very homogeneous layerscan be reached in case no depletion effects of the activated speciesradially outwards occur.

According to further advantageous modified embodiments of the inventionturntables are provided on one or on both electrodes, on the annularelectrode and/or on the oppositely located sheet electrode, in suchmanner as to be rotatable by a gear wheel which is rigidly connected tothe electrode(s) and which can be driven via an electrically insulatingintermediate member and at least one rotary bearing introduced into theevacuatable chamber in a vacuum-tight manner from without.

According to further advantageous modified embodiments of the inventiona temperature moderating labyrinth system is provided both in theannular electrode and in the sheet electrode and is connected via adetectable connection flange to a tempering medium circuit. Herewith theadvantage is achieved that the desposition rate can be influenced viathe temperature.

According to further advantageous modified embodiments of the inventionresistance-heated plates can be provided as an additional heating bothon the annular electrode and on the sheet electrode, the heating currenttransmission occurring by sliding ring contacts. Herewith the advantageis associated that processes can also be carried out in which a givenminimum substrate temperature is required.

When the device according to the invention is to be used for a highfrequency cathode sputtering process, according to an advantageousfurther embodiment of the invention the electrodes (annular and sheetelectrodes) can be provided with screenings which are connected to earthpotential. The performance of a plasmachemical vapour deposition processby means of the device according to the invention will be described withreference to an example for the manufacture of a plasma-polymerizedlayer on a substrate, the method being carried out so that at least onesubstrate to be coated is laid on one of the electrodes (sheet electrodeor annular electrode) in the evacuatable chamber and the starting gasconsisting of at least one monomeric process gas from which a layer ofplasma-polymerized material can be deposited on the substrate(s) by highfrequency excitation of the gas phase molecules, and optionally at leastone inert carrier gas is introduced into the chamber via the device forleading-in gaseous substances. According to an advantageous modifiedembodiment of the method according to the invention the layer ofplasma-polymerized material is formed so that as a monomeric process gasat least one such gas is supplied from which polymerizedSi:N:O:C:H-containing compounds can be formed. Hexamethyl disilazane ispreferably supplied as a monomeric process gas.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing FIG. 1 is a sectional view of a first embodiment of theinvention.

FIG. 2 is a sectional view of a second embodiment of the invention.

FIG. 3 is a sectional view of a device of the invention used as an RFcathode sputtering device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described in greater detail withreference to the drawing.

FIG. 1 shows a device for coating a substrate having an evacuatablechamber 1 with a sheet electrode 3 and an annular electrode 5 whichbears on a bipartite insulator block. The annular electrode 5 has acentral aperture 11. The insulator block arranged below the annularelectrode has a first upper portion 7 adjoining the annular electrodeand comprising a central aperture 13 which preferably widens conicallyand whose diameter adjoining the annular electrode 5 corresponds to thediameter of the central aperture 11 in the annular electrode 5. The part7 of the insulator block comprises a further aperture 15 which opensinto the central aperture 13, extends approximately at right anglesthereto, and can be closed by means of a stopper 17. The portion 7 ofthe insulator block is present on a second portion 9 of the insulatorblock which likewise comprises a central aperture 19 which preferablywidens conically and whose diameter on the side of the first portion ofthe insulator block corresponds to the diameter of the central aperturein the first portion 7 of the insulator block at that area. Via the ductformed from the central apertures 11, 13 and 19, gases can be drawn fromthe reaction space via a vacuum pump (not shown) connected to a pumpnozzle 21. Process gases are supplied to the evacuatable chamber 1 via amulti-chamber annular distributor 23; the gases emanate freely from themultichamber annular distributor 23 in the direction of the arrows intothe reaction space. The multichamber annular distributor 23 comprises atleast one connection 25 for the inlet of process gases (four connectionnozzles are shown in the drawing) from which the process gases enterchambers 27 present above the connections 25 and communicating with eachother, via apertures, from which chambers the processes gases enter thereaction space via a plurality of smaller apertures 29 and can be drawnagain out of the reaction space via the system of apertures 11, 13 and19 in the direction of the arrows 31.

The uniformly distributed gases are hence drawn off centrally via theelectrode surface of the annular electrode 5. A turntable 33 is providedon the annular electrode 5 and can be rotated by a gear wheel 35 whichis rigidly connected to the annular electrode and which is engaged by apinion not shown, which pinion can be driven via an electricallyinsulating rack-compensating intermediate member and a rotary bearing 39which can be actuated from without and is passed in a vacuum-tightmanner from without through the bottom plate 37 of the chamber 1.

Construction of the turntable present on the annular electrode: the gearwheel 35 with z=360 and m=1 (z=teeth; m=module) provided with anextension (not shown) of a diameter of 160×20 and a central aperturehaving a diameter of 150 mm, is provided on the annular electrode 5 bysimple mounting. The driving is carried out via a pinion mountedlaterally of the electrode with z=20 which is driven from without viathe rotary bearing 39. The maximum speed is approximately 2 rpm. Theannular electrode 5 has a temperature moderating labyrinth 41 which canbe connected via a lateral rapidly detachable connection flange 43 to atempering medium circuit. The connection flange 43 simultaneously servesas a connection to the RF-generator system and is led out in avacuum-tight and electrically insulated manner from the evacuatablechamber 1 via the base plate 37.

In order to ensure a good thermal coupling to the tempered annularelectrode 5, bronze and hard chromium are used as material combinationsof the sliding surfaces. Silicon oil improves the thermal contact andthe sliding properties. A turntable (not shown) may also be provided onthe sheet electrode 4. Structurally the turntable of the upper plateelectrode 3 is constructed as that of the lower annular electrode 5.

As a result of the suspending arrangement of the sheet electrode 3, thebearing must be constructed so as to be form-coupled; for that purpose,a track ring which is conical on the side remote from the process may bemounted on the circumference of the suspended sheet. This ring maysupport track roller racks, radially as well as axially, that aremounted on the turntable and position the plane face of the turntableagainst the surface of the sheet electrodes 3, so that on one hand agood thermal conductivity takes place and on the other hand the rotationis not hampered. The material combination of the bearing surfaces inthis case also is bronze on hard chromium, and silicon oil may also beused to improve the sliding properties and the thermal conductivity.

FIG. 2 shows a modified embodiment of the device according to theinvention in which process gases are supplied to the evacuated space 1via gas inlets 45 led through the base plate 37 of the evacuated chamber1 in a vacuum-tight manner and opening into the further aperture 15which opens into the central aperture 13 of the portion 7 of theinsulator block from which the stoppers 17 have been removed. For theconstruction of the FIG. 2 device the second part 99 of the insulatorblock is a solid plate and the area of the central aperture 11 in theannular electrode 4 adjoining the reaction space is covered with aperforated cover plate 47, for example of copper sheet. The reactiongases which have reached the reaction space via the central aperture 13in the portion 7 of the insulator block and the perforated cover plate47 in this embodiment are not removed via the apertures 11, 13 and 19,but they are removed by the vacuum pump on the outside of the insulatorblock 99 via slots 49 provided laterally therein and the additivecross-section of which is larger than the cross-section of the nozzle 21of the vacuum pump.

The severing of the insulator block into the portions 7, 9 and 99 thusenables two forms of operation of the device: according to FIG. 1 thecentral aperture in the insulator block is free so that the pumpingsystem removes the gases introduced via the annular gas distributor fromthe reaction space through said aperture.

According to FIG. 2 the central suction is interrupted. The processgases flow through the available apertures in the upper insulatorportion and reach the reaction space centrally through the perforatedcover sheet. They are removed by the pumping system via the electrodefrom the inside to the outside and through laterally provided slots inthe lower exchanged insulator portion in the form of a plate without acentral aperture.

The arrangement of substrates may occur on both electrodes. Bothelectrodes can be switched electrically at RF potential or earthpotential. Positioning may be done by simply providing them on theannular electrode, while for the positioning on the upper sheetelectrode a substrate holder plate is required. Both electrodes may beprovided with turntables which permit a good layer thicknesshomogeneity.

Under deposition conditions which require a temperature up to 500° C.the further additional element may be a heating plate provided both onthe lower annular electrode 5 and also on the upper sheet electrode 3 inthe form of a resistance-heated plate (53). The heating currenttransmission occurs via screened sliding ring contacts.

Radiation sheets 57 are advantageously provided between the electrode(s)3 and the resistance-heated plates 53 for thermal separation. In thiscase substrates are placed on the resistance-heated plates.

While using the device according to the invention as shown in FIG. 1 apolymer layer manufactured from hexamethyldisilazane (HMDSN) wasdeposited on substrates which with a layer thickness of d=0.6 μm reachesa radial layer thickness homogeneity of ±1% with an envisaged length ofl=60 mm; a radial layer thickness homogeneity of ±5% was achieved withan envisaged length of l=140 mm.

The following process parameters were used: the substrates were providedon the upper sheet electrode 3; the electrode spacing H between thesheet electrode 3 and the annular electrode 5 was adjusted at H=50 mm.Substrate temperature T_(S) =35° C.; monomer gas pressure P_(HMDSN) =2Pa; carrier gas pressure P_(argon) =3 Pa; output surface density N=0.5W/cm² ; deposition rate d=40 nm/min.

This example shows that with the present device a particularly gooduniformity of the layer thickness of the produced layers can beachieved. In spite of an increased deposition rate at which usually alayer thickness gradient occurs due to the depletion of the excitedspecies, the above-given good values for the layer thickness homogeneitywere achieved.

FIG. 3 shows a device according to the invention for use as anRF-cathode sputtering device. For this purpose it is necessary to screenthe electrodes 3, 5 from the inner wall of the evacuated chamber 1 bytwo screening rings 51 which are at earth potential.

What is claimed is:
 1. A device for providing a coating on a substrateby means of a plasma chemical vapor deposition or cathode sputtering,said device comprising a first angular electrode provided with anaperture extending along a central axis and axially fixed in anevacuatable chamber provided with a second counter sheet electrodespaced from and opposing said first electrode, means for introducinggaseous substances into said chamber, means for applying a voltage tosaid electrodes to produce plasma in said chamber, and said chamberbeing further provided with a bipartite insulator block having an upperfirst portion adjoining said first electrode and provided with a centralaperture corresponding to the central aperture of said first electrodeand having a second portion immediately adjoining said first portionbearing on the base of said evacuatable chamber and positioned over aconduit means for conducting gaseous material from said chamber to avacuum pump means, said conduit means extending into the base of saidevacuatable chamber.
 2. A device as claimed in claim 1, characterized inthat the first portion (7) of the insulator block comprises at least onefurther aperture (15) which opens into the central aperture (13) andextends approximately at right angles thereto.
 3. A device as claimed inclaim 1, characterized in that when the device is used as an RF cathodesputtering device the electrodes can be provided with screens (51) whichare at earth potential.
 4. A device as claimed in claim 1, characterizedin that the second portion (99) of the insulator block is a solid plate.5. A device as claimed in claim 2, characterized in that the furtheraperture(s) (15) can be closed on the side to the reaction space of theevacuatable chamber (1).
 6. A device as claimed in claim 1,characterized in that the central aperture (13) of the first portion (7)of the insulator block on its side adjoining the annular electrode (5)has a diameter which correponds to the diameter of the central aperture(11) of the counter sheet electrode, and widens in the direction to thesecond portion (9, 99) of the insulator block.
 7. A device as claimed inclaim 1, characterized in that the second portion (9) of the insulatorblock has a central aperture (19) which on the side adjoining the firstportion (7) of the insulator block has a diameter which corresponds tothe diameter of the central aperture (13) of the first portion (7) ofthe insulator block on said side and which enlarges in the direction tothe base plate (37) of the evacuatable chamber (1).
 8. A device asclaimed in claim 1, characterized in that the device for introducinggaseous substances into the evacuatable chamber (1) is a multichamberannular distributor (23) in which reaction gases can be introduced fromwithout and can freely reach the reaction space of the chamber.
 9. Adevice as claimed in claim 2, characterized in that the means forintroducing gaseous substances into the evacuatable chamber (1) are gasinlets (45) led through the base of said chamber in a vacuum-tightmanner and opening into the further aperture (15) which opens into thecentral aperture (13) of the insulator block and extends at right anglesthereto.
 10. A device as claimed in claim 1, characterized in that aturntable (33) is provided on at least one of the electrodes which canbe rotated by a gear wheel (35) which is rigidly connected to theelectrode and which can be driven via an electrically insulatingintermediate member and a rotary leadthrough (39) introduced into theevacuatable chamber (1) from without in a vacuum-tight manner.
 11. Adevice as claimed in claim 8, characterized in that the multichamberannular distributor (23) comprises at least one connection (25) for theinlet of process gases from which the process gases reachintercommunicating chamber (27) via apertures in the multichamberannular distributor present above the connection(s), therefrom theprocess gases reach, via a number of apertures (29), the reaction spaceof the evacuatable chamber (1) present above the multi-chamber annulardistributor and can be drawn out of the evacuatable chamber again viathe central aperture (11) in the annular electrode (5) and the centralapertures (13, 19) in the insulator block.
 12. A device as claimed inclaim 1, characterized in that in at least one of the electrodes atempering labyrinth system (41) is provided which is connected to atemperature medium circuit via a detachable connection flange (43). 13.A device as claimed in claim 1, characterized in that a high frequencygenerator for producing the electric voltage is provided withconnections on the annular electrode (5) and/or the sheet electrode (3).14. A device as claimed in claim 13, characterized in that theconnection flange (43) for the tempering medium is also connected to thehigh frequency generator.
 15. A device is claimed in claim 4,characterized in that the central aperture (11) on the annular electrode(5) on the side facing the reaction space can be covered with aperforated plate (47) via which the reaction gases flow into thereaction space.
 16. A device as claimed in claim 1, characterized inthat both portions of the insulator block consist of an electricallyinsulating material suitable for high frequency application.
 17. Adevice as claimed in claim 16, characterized in that both portions (7,9, 99) of the insulator block consist of polytetrafluoroethylene.
 18. Adevice as claimed in claim 1, characterized in that the sheet electrode(3) for moving the electrode in the axial direction is connected via aninsulator to a sliding lead-through (55) introduced into the evacuatablechamber (1) in a vacuum-tight manner.
 19. A device as claimed in claim1, characterized in that substrates can be placed both on the annularelectrode (5) and on the sheet electrode (3).
 20. A device as claimed inclaim 4, characterized in that slots (49) are provided in the secondportion (99) of the insulator block via which the reaction gases can bedrawn by the vacuum pump.
 21. A device as claimed in claim 10,characterized in that the sliding properties between the turntable(s)(33) and the electrode(s) are improved by a readily heat-conductinglubricant provided between said turntable(s) 33 and said electrodes. 22.A device as claimed in claim 1, characterized in that as an additionalheating means resistance-heated plates (53) may be provided on theannular electrode (5) and on the sheet electrode (3), the heat flowtransmission occurring by sliding ring contacts.
 23. A device as claimedin claim 22, characterized in that radiation sheets (57) may be mountedbetween the turntable(s) (33) and the resistance-heated plate(s) (53).24. A device as claimed in claim 19, characterized in that thesubstrates can be placed on the resistance-heated plates (53).